Many types of automated machinery require drive mechanisms to reciprocate machine elements within a defined range of motion. One specific example of such drive mechanisms are those used in tufting machines to reciprocate the needle bar. Advances in the production capacity of tufting machines generally has followed improvements in the needle bar drive mechanisms. The speed at which these drive mechanisms rotate generally dictates the speed of reciprocation of the needle bar, which primarily determines production capacity. Therefore, increasing the speed of the needle bar drive mechanism has been the primary focus of attempts to improve the operation of tufting machines.
For example, U.S. Pat. No. 4,665,845 to Card et al. discloses a tufting machine needle drive mechanism which includes individual needle drive assemblies driven by the main drive shaft. These individual drive assemblies are spaced along the main shaft, and are driven in the same direction as the main shaft by timing belts. This arrangement greatly improved the production capacity of the tufting machines then in use, by increasing the revolutions per minute of the drive mechanism from about 750 to 1,000 rpm to over 1,300 rpm. The rotational speed at which this type of drive mechanism could operate, however, was limited to some extent by the multidirectional vibrational forces caused by the many reciprocating elements of the machine, such as the loopers and knives.
An improvement to such drive mechanisms is disclosed in U.S. Pat. No. 5,287,819 to Beatty et al. This drive mechanism includes separate needle drive assemblies, but also includes additional mechanisms which offset many of the vibrational forces caused by the reciprocating machine elements. Specifically, the drive mechanism disclosed in this patent includes two main drive shafts, one driven in counterrotational movement by the other, with the individual needle drive assemblies also being driven in opposite directions by their respective drive shaft. This counterrotational movement, together with the placement of counterweights along the main drive shaft, greatly reduces the overall vibration in the tufting machine during operation. This configuration and its associated reduction in vibration, make it possible for this machine to operate of speeds in excess of 2,000 rpm, greatly increasing machine performance and production capacity.
While this machine represents a significant improvement over the drive mechanisms of the prior art, its design requires a second drive shaft and associated support and journaling elements. The design also requires reversing drives at each end for imparting counterrotational movement to the second drive shaft. Additionally, the design, while safe, efficient and reliable, necessitates the need to accurately time the rotation of the respective drive shafts in order to control the timing of the elements driven therefrom.